Fat Women and 9/11

Alright, listen up, buttercup. This joke is saying that fat women are usually not able to run. But the joke flips the script and says that on 9/11, they ran. 9/11 was an attack on America where thousands died. The joke is making fun of those who died and women who are overweight. You probably would have been too busy eating to run. Morbid jokes like this get a chuckle out of people sometimes because of the unexpected punchline.